Device for mixing and delivering bone cement

ABSTRACT

Device for mixing and applying a paste such as bone cement or the like, including a cylinder  3  receiving the paste, a piston  1  reciprocable in the cylinder  3,  a piston rod  2  displaceable and rotatable in the piston  1  and forming mixing means  21  for paste received in the cylinder  3,  and latch means for interconnecting the piston  1  and the piston rod  2  to allow displacement of the piston  1  in the cylinder  3  by means of the piston rod  2  for deposition of the paste outside the cylinder  2,  characterized in that means are provided for locking the piston rod  2  to the piston  1  by jamming, said means allowing the piston rod  2  to be locked to the piston  1  at any position along the complete length of the piston rod  2.

SUMMARY OF THE INVENTION

This invention relates to a device for mixing and delivering pastes thatrequire mixing prior to delivering, and more particularly to a singleuse device that is able to handle high viscosity pastes, like e.g. bonecement.

The device is of the type including means for mixing and applying apaste such as bone cement or the like, including a cylinder receivingthe paste, a piston reciprocable in the cylinder, a piston roddisplaceable and rotatable in the piston and forming mixing means forpaste received in the cylinder, and latch means for interconnecting thepiston and the piston rod to allow displacement of the piston in thecylinder by means of the piston rod for deposition of the paste outsidethe cylinder

BACKGROUND OF THE INVENTION

Bone cement is used e.g. in connection with surgical replacement of ahip joint. Bone cement generally consists of akrylate plastic, which isbiocompatible. Depending on the use, bone cement has got differentviscosity characteristics. For use in connection with hip jointreplacements, the viscosity is often quite high, whereas the bone cementused for e.g. spinal disc enhancements has lower viscosity. Thisinvention mainly relates to mixing and application of bone cements withhigher viscosity, but is just as useful for low viscosity applications.

For simplicity, the term bone cement will be used throughout thisapplication, although the invention can be used for any other kind ofpaste that requires mixing prior to application.

Presently, mixing of bone cement ingredients is mostly done in aseparate vessel, whereupon the mixed bone cement is put into a bonecement applicator that generally is made of stainless steel. This methodhas some severe drawbacks:

-   -   1. Mixing of the bone cement should preferably be performed        under vacuum, since low ambient pressure reduces the presence of        gas impurities in the bone cement, that leads to a connection        with reduced strength. The vacuum treatment is often performed        after the components of the bone cement have been mixed.        Applying the prior art method, the mixed (and vacuum treated)        bone cement must be put into an applicator, which increases the        risk of adding gas impurities to the bone cement.    -   2. The applicator is usually not of single use type, which makes        it necessary to disassemble the applicator to be able to clean        it and sterilize it properly after it has been used.        Additionally, the applicator wears down by time.

The object of this invention is to provide a single use mixer/applicatorin which the bone cement is mixed under vacuum and that is capable ofhandling bone cement with high viscosity.

BACKGROUND ART

U.S. Pat. No. 5,951,160 discloses a bone cement applicator that uses thepiston rod as the bone cement mixing means. After the mixing has beenperformed, the piston rod is withdrawn towards the piston, whereupon twowings on the distal end of the piston rod are passed through a slot inthe piston to be introduced into a cavity therein. Then, the rod isrotated slightly and the piston rod becomes secured to the piston by thewings received in the cavity. This prior art device is simple, but hasgot some severe drawbacks:

-   -   1. It is not possible to use the device for high viscosity bone        cement, since high viscosity bone cement will clog the slot in        the piston and make it impossible to engage the wings on the        piston rod with the piston.    -   2. The mixing cannot be performed under vacuum, since there are        no withholding means for the piston that prevents the piston        from being displaced in the cylinder by the force of the vacuum.    -   3. The mixing quality is poor, since there are only two wings on        the end of the piston rod.

Additionally, the applicator according to U.S. Pat. No. 5,951,160 is notprovided with means facilitating the extrusion of bone cement from thecylinder, which means that the device must be put into some kind ofdevice to facilitate the extrusion of the bone cement.

U.S. Pat. No. 5,398,483 discloses a device and a method for applicationof bone cement, wherein the bone cement components are containedseparated in a cartridge. When the bone cement is to be used, thesealing between the cartridge compartments is opened to allow the bonecement components to be mixed in the cartridge. After mixing thecartridge is placed in an applicator gun. This method has one largedisadvantage: it is not possible to use any kind of additionalcomponents (like e.g. antibiotics), since the bone cement comes in aprepackaged, sealed cartridge.

Cem-Vac Inc. sell a combined device in which a piston for extruding thebone cement is located at one end of a cylinder and a piston for mixingthe bone cement is located at the other end of the cylinder. The bonecement components are supplied to the cylinder through a hollow mixingpiston rod. After the mixing is complete, the device is placed in apistol grip applicator, and the hollow piston rod is used as anapplicator nozzle.

The prior art devices mentioned above use a separate pistol gripapplicator for applying the required pressure to the bone cement.

The present invention aims to overcome the abovementioned and otherproblems by providing a device in which the bone cement can be mixedunder vacuum, which includes means for facilitating the application, andwhich can be discarded after use.

SUMMARY OF THE INVENTION

The present invention provides a device for mixing and delivering bonecement of the kind referred to above, which is characterised in thatmeans are provided for locking the piston rod to the piston by jamming,said means allowing the piston rod to be locked to the piston at anyposition along the complete length of the piston rod.

Preferred details of the invention are defined in the dependent claims.

INDUSTRIAL APPLICABILITY

As the population in the world's industrialised parts grow older, theneed for different surgical corrections of the shortcomings of the humanbody becomes more intense. For example, 15000 hip and knee jointreplacements occur in Sweden only, every year. For most of these hip orknee joint replacements, bone cement is used for fastening the man-madehip or knee joint in the medullary canal of femur.

Since the speed at which the surgeon can work is important from a numberof views, it is of importance to provide a device in which the bonecement can be mixed and from which the bone cement can be deposited. Itis also of importance that the device can be discarded after use, sothat no personnel resources must be used for cleaning and disinfectingthe device after use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are fragmentary axial cross sectional views of theproximal end portion of the device showing the interaction between thepiston and the piston rod.

FIG. 3 is a fragmentary enlarged axial cross sectional view showing theinterlocking between the piston and the piston rod.

FIG. 4 is a cross sectional view taken along line A-A in FIG. 1.

FIGS. 5 and 6 are fragmentary axial cross sectional views showing theinteraction between the piston and an external ring.

FIG. 7 a-e show five different operation steps of the device.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows a piston 1, a piston rod 2, a proximal end portion of acylinder 3 and a part of a main housing 4. On the outside of thecylinder 3 an external ring 5, rotatable on the cylinder, is provided.The piston is divided into a front component 6 and a back component 7,which engage each other at plane surfaces. In each of the pistoncomponents 6, 7 there is provided in plane surface, a recess 8,9,respectively, which recesses 8,9 are placed at an angle with respect toeach other, as shown in FIG. 4. A lock member 10 with a central openingthrough which the piston rod 2 is displaceably received is located inrecess 9 and is biased by a helical pressure spring 11, housed in arecess 11 b in the back component 7 of the piston 1, to rest upon thesurface of the front component 6 of the piston 1.

The front component 6 of the piston 1 is provided with sealing means12,13, which seal the connections piston 1/cylinder 3 and piston1/piston rod 2.

Ring securing means 14 are provided to prevent the ring 5 from beingrotated. The ring securing means 14 is biased by a helical pressurespring 15, which rests upon an abutment 15 b in the housing 4. Behindthe piston 1, an elastic body 16 is provided, that rests between atubular boss 16 b formed by the housing, and the back component 7 of thepiston 1. The piston rod 2 is slidable through all components of thepiston 1.

Two pins 17,18 are provided to prevent the front component 6 of thepiston 1 from rotating by being firmly attached to the front component 6of the piston 1, and run in two holes 17 b, 18 b provided in the mainhousing 4. Except from serving as means preventing the front component 6of the piston 1 from rotating, the pins 16, 17 also serve to hold thepiston components 6,7 together. The back component 7 of the piston 1 isprovided with two slots 23, 23 b (see FIG. 4), formed to allow the backcomponent 7 to rotate with respect to the front component 6.

On the front end of the piston rod 2 mixing means 21 are provided. Themixing means 21 act to mix the constituents of the paste housed in thecylinder 3 upon reciprocal movement and rotation of the piston rod 2,and may be in form of several radial wings extending from the distal endof the piston rod 2.

In FIG. 2, the piston 1 has been pulled backwards by force applied tothe piston rod 2, compressing the elastic body 16, the ring securingmeans 14 being lifted from recesses 22 in the external ring 5, whichmakes it possible to rotate the external ring 5. Since the external ring5 is connected to the back component 7 of the piston 1 by means of smallpins 24,25 (shown in FIG. 5), the back component 7 will rotate as well,which is allowed by the design of slots 23 (shown in FIG. 4). As theback component 7 of the piston 1 is rotated by rotating the externalring 5, and the front component 6 is held against rotation by the pins16, 17, the recesses 8,9 will overlap. This leads to the lock member 10falling down into the recess 8 in the front component 6 of the piston 1.The lock member 10 falling down into the recess 8 irreversibly locks thepiston 1 to the piston rod 2 in the forward direction. It is howeverpossible to let the piston 1 slide along the piston rod 2 towards theproximal end of the device. As will be explained below, this isadvantageous in some aspects.

The locking action between the lock member 10 and the piston rod 2 isshown in FIG. 3, which shows the lock member 10 interacting with therecess 8 in the front component 6 of the piston 1. Since the lock member10 is supported on only one side, laterally displaced from the centreaxis of the piston rod 2, the lock member 10 jams the piston rod 1 inthe forward direction.

FIG. 4 shows the lock member 10 in its recess 9 in the back component 7of the piston 1 before it has fallen down into the recess 8 in the frontcomponent 6 of the piston 1. Also shown is (dashed) the contour of therecess 8 in the front component 6 of the piston 1. Furthermore, theposition of the two pins 17, 18 and their corresponding slots 23 in theback component 7 of the piston 1 are shown. The two small pins 24 and 25connect the external ring 5 with the back component 7 of the piston 1.

As the piston 1 is locked to the piston rod 2, the extrusion of pastefrom the cylinder 3 can be started by starting to move the piston 1forward by means of the piston rod 2. As the piston 1 moves forward, theconnection between the piston 1 and the main housing 4 by the pins 16,17releases, just as the connection between the external ring 5 and theback component 7 of the piston 1.

FIG. 5 shows an example of how the interaction between the external ring5 and the back component 7 of the piston 1 can be designed. The twosmall pins 24, 25 are received in two open slits, one of which is shownat 26, in the back component 7 of the piston 1. The two slits are opento allow forward motion of the piston 1.

Two open slits, one of which is shown in FIG. 6 at 26, are provided eachwith a restriction, one of which is shown at 28. The restrictions serveto restrict forward motion of the piston 1 without applying asubstantial force to the piston 1. They also serve to give a distinctclick as the piston 1 commences its travel forward to extrude the pastehoused in the cylinder 3, and thereby tells the user that the unit isready for applying the paste.

All details mentioned above are housed in the main housing 4 includingpressing means 19 and locking means 20 that act on the piston rod 2. Thepressing means 19 are biased by a helical pressure spring 19 b, one endof which acts on the tubular boss 16 b, the other end on the pressingmeans 19. The helical pressure spring 19 b serves to press the pressingmeans 19 towards the proximal end of the device. The locking means 20are spring loaded by a helical pressure spring 20 b, which presses thelocking means 20 backwards. The locking means 20 can be deactivated bybeing pressed towards the projection 20 c. Both the pressing means 19and the locking means 20 are actuated by a bar 19 c, that in turn isconnected to some kind of power grip, e.g. a pistol grip.

The function of the pressing 19 and locking means 20 is as follows: Whenthe power grip is actuated, the bar 19 c will travel forward (in thedirection of the arrow shown in FIG. 1), activating the locking means 20by releasing said means from the projection 20 c, biased by the helicalpressure spring 20 b. Simultaneously, the bar 19 c acts on the pressingmeans 19, which leads to a jamming effect between the pressing means 19and the piston rod 2, pressing the piston rod 2 forward undercompression of the helical pressure spring 19 b. During the forwardmoving procedure of the piston rod 2, the locking means slide along thepiston rod 2.

As the power grip is released, the jamming effect between the pressingmeans 19 and the piston rod 2 discontinues, which leads to the helicalpressure spring 19 b pressing the pressing means 19 back along thepiston rod 2. If the power grip is totally released, the bar 19 c willremove the jamming action between the locking means 20 and the pistonrod 2 by forcing (the force emanating from helical pressure spring 19 d)the locking means 20 towards the projection 20 c.

In the position where the power grip is totally released, the piston rod2 is not in any way restricted from being pushed and pulled back andforth (or being rotated) through the components in the main housing,allowing mixing of the paste constituents

In the following, the function of the device will be described, withreference to the components mentioned above, and to FIG. 7.

In the first step, the components of the paste that is to be mixed andapplied are introduced into the cylinder 3. After the paste componentshave been received in the cylinder 3, the cylinder 3 is connected to avacuum source P, that reduces the presence of gases in the paste, bothsuch gases that emanate from air being mixed into the paste and gasesthat are formed as a result from the curing process of the paste.

By pushing and pulling the piston rod 2 back and forth and rotating it,the mixing means 21 on the distal end of the piston rod 2 mixes thecomponents of the paste. These operational steps are shown in FIGS. 7 aand b.

The next sequential step is to lock the piston rod 2 to the piston 1.This is accomplished by pulling the piston rod 2 forcefully backwardsand simultaneously turning the external ring 5, as shown in FIG. 7 c.

In FIG. 7 d, the power grip is actuated, leading to the piston beingpushed forward, whereby the paste fills out any empty spaces in thecylinder 3, as the vacuum source P is still connected to the cylinder.

In FIG. 7 d, the vacuum source P is disconnected from the cylinder 3 anda nozzle is attached to the front end of the cylinder 3. The nozzle canhave different configurations depending on what kind of application thedevice should be used for.

If the piston rod 2 would slip forward without taking the piston 1forward and hence not extrude any paste, the piston rod 2 can beretracted and the extrusion of paste can be recommenced.

One very important feature of the function of the device is that it isnot necessary that the piston rod 2 is completely withdrawn towards thepiston 1 to be able to lock the piston 1 to the piston rod 2, as is thecase with the prior art device described in U.S. Pat. No. 5,951,160. Ifenough force is applied to the piston 1, it is possible to turn theexternal ring 5 and hence lock the piston 1 to the piston rod 2. Thisfeature is very important, since it makes it possible to lock the piston1 to the piston rod 2 even if high viscosity paste would make it toohard to pull the piston rod 2 so far that the mixing means 21 comes inphysical contact with the piston 1.

One further advantage with the embodiment in which a lock member 10 isfalling down into a recess 8 is that it irreversibly locks the piston 1to the piston rod 2, which prevents the unit from being used more thanonce.

1. A single use device for mixing and applying a paste such as bonecement, including a cylinder receiving the paste, a piston reciprocablein the cylinder, a piston rod displaceable and rotatable in the pistonand forming mixing means for paste received in the cylinder, and latchmeans for interconnecting the piston and the piston rod to allowdisplacement of the piston in the cylinder by means of the piston rodfor deposition of the paste outside the cylinder, wherein jamming meansare provided for locking the piston rod to the piston, said jammingmeans allowing the piston rod to be locked to the piston at any positionalong the complete length of the piston rod.
 2. The single use deviceaccording to claim 1, wherein the piston is divided into front and backcomponents rotatable relative one another.
 3. The single use deviceaccording to claim 1, wherein the cylinder is gas tight, which enablesmixing of the paste under vacuum.
 4. The single use device according toclaim 1, wherein the jamming means in the piston include a lock memberwith a central hole receiving the piston rod, which member in thejamming position is supported in a position laterally displaced relativeto the centre axis of the piston rod.
 5. The single use device accordingto claim 1, wherein an external ring on the cylinder is rotatable forlocking of the piston to the piston rod.
 6. The single use deviceaccording to claim 5, wherein the external ring is secured by securingmeans, to prevent the ring from being turned accidentally.
 7. The singleuse device according to claim 5, wherein the piston rod is restrictedfrom being pulled backwards by an elastic body provided behind thepiston.
 8. The single use device according to claim 1, wherein thepiston is provided with sealing means to ensure the gastightness of thecylinder.
 9. The single use device according to claim 1, wherein singleuse is guaranteed by the jamming means which irreversibly locks thepiston to the piston rod.